(1) Field of the Invention:
This invention relates to a novel steroid ester as well as cosmetics and ointments containing the same, and more particularly to an ester between a certain kind of steroid and an .alpha.-branched carboxylic acid as well as cosmetics and ointments containing the same.
(2) Description of the Prior Art:
Esters such as steroid esters are widely used as an oil phase material or base material of cosmetics for the skin or hair, or of ointments. For example, stearic acid ester or oleic acid ester of cholesterol is contained in stick-like cosmetics such as lipstick, eyeshadow and stick pomade as well as in cosmetic cream, ointment, etc. These linear fatty acid esters of cholesterol are excellent in water-embracing or -encapsulating property and emulsifying property, exhibit affinity with the skin, and are not irritative. These properties render the esters desirable for use as an oil phase material or additive of, for example, cosmetics or ointments. However, these esters are undesirably solidified at temperatures near the human skin temperature. For example, cholesteryl stearate has a melting point of 75.degree. to 85.degree. C., with cholesteryl oleate having a melting point of 40.degree. to 45.degree. C., with the result that the cosmetics containing these esters give uncomfortable feel to the user when applied to the skin. It should also be noted that these esters are decomposed into cholesterol and fatty acids under the action of lipase present on the skin.
Japanese Patent Disclosure (Kokai) No. 52-79030 teaches the idea of mixing into cosmetics esters of fatty acids such as stearic acid and oleic acid with phytosterol, which resembles cholesterol in chemical structure, or its hydrogenated derivative. The above-noted prior art certainly teaches that the particular ester is not irritative to the skin and can be used comfortably, but does not teach at all the properties of the ester such as water-embracing property, emulsifying property, water-holding property and resistance to hydrolysis.
The present inventors have examined the resistance to hydrolysis of cholesteryl stearate, cholesteryl oleate, phytosteryl stearate and phytosteryl oleate under the ordinary hydrolyzing (or saponifying) conditions of oil and fat. Specifically, these esters were heated at 80.degree. to 85.degree. C. within a 1/2 N alcoholic KOH solution, with the result that any of these esters was completely hydrolyzed within 1 hour of heating. To be brief, the conventional linear fatty acid esters of steroid are unsatisfactory in resistance to hydrolysis.
It is further required that an oil phase material contained in, for example, cosmetics be high in water-embracing property. "Water-embracing property" means the capability of embracing and holding water in an oil phase material. An oil phase material high in water-embracing property permits decreasing the amount of surfactant contained in the cosmetics and enables water to be retained on the skin surface, giving the user a moist feel. Lanolin certainly exhibits a high water-embracing property, but produces allergy effect. Thus, it is a matter of serious concern in this field to develop an oil phase material of cosmetics which can be used in place of lanolin. Japanese Patent Disclosure (Kokai) No. 52-95700 teaches the idea of removing the allergy component from lanolin, but the resultant material leaves room for further improvement. A linear fatty acid ester of cholesterol is also known to exhibit a high water-embracing property, but fails to provide a satisfactory oil phase material of cosmetics.